How do you design MIMO antennas?

MIMO (multiple-input multiple-output) uses several antennas at each end of a link to multiply capacity through spatial multiplexing or improve reliability through diversity. Foschini and Gans and Telatar showed that, in rich scattering, capacity C = log₂det(I + (ρ/N_t)HH^H) grows roughly linearly with min(N_t, N_r).^[1][2] MIMO antenna design therefore aims for high efficiency, low mutual coupling and low envelope correlation between ports.^[3]

What is the envelope correlation coefficient?

ECC measures the similarity of two antennas’ complex far-field patterns over the sphere, weighted by the incoming-wave distribution; values below about 0.5 are commonly considered adequate for diversity and MIMO. For lossless antennas in uniform scattering it can be computed from S-parameters: ρ_e = |S₁₁*S₁₂ + S₂₁*S₂₂|² / [(1−|S₁₁|²−|S₂₁|²)(1−|S₂₂|²−|S₁₂|²)].^[4] Real antennas have loss, so pattern-based ECC is preferred.

How is decorrelation achieved?

• Spatial separation (≥ λ/2 in rich scattering, more at base stations with narrow angular spread).
• Polarization diversity (e.g., ±45° slant).
• Pattern diversity: different beam directions or modes on the same chassis.

^[5][3]

How are MIMO antennas tested?

Metrics include isolation, ECC, total efficiency and multiplexing efficiency; system-level MIMO OTA testing in reverberation chambers or multi-probe anechoic chambers emulates channel models such as those of 3GPP TR 38.901.^[6][7]

Frequently asked questions

See also

• Mutual coupling
• Antenna diversity
• Massive MIMO
• Cellular 4G/5G antennas

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

1. “On Limits of Wireless Communications in a Fading Environment when Using Multiple Antennas”. G. J. Foschini and M. J. Gans, Wireless Personal Communications, vol. 6, no. 3, pp. 311-335. March 1998.
2. “Capacity of Multi-antenna Gaussian Channels”. I. E. Telatar, European Transactions on Telecommunications, vol. 10, no. 6, pp. 585-595. 1999.
3. “Foundations of MIMO Communication”. R. W. Heath Jr. and A. Lozano, Cambridge University Press. 2018.
4. “Exact Representation of Antenna System Diversity Performance from Input Parameter Description”. S. Blanch, J. Romeu and I. Corbella, Electronics Letters, vol. 39, no. 9, pp. 705-707. May 2003.
5. “Antenna Diversity in Mobile Communications”. R. G. Vaughan and J. B. Andersen, IEEE Transactions on Vehicular Technology, vol. 36, no. 4, pp. 149-172. November 1987.
6. “3GPP TR 38.901: Study on channel model for frequencies from 0.5 to 100 GHz”. 3GPP. current release.
7. “Test Plan for Wireless Device Over-the-Air Performance”. CTIA Certification. current version.